687691 has 2 divisors, whose sum is σ = 687692. Its totient is φ = 687690.

The previous prime is 687683. The next prime is 687707. The reversal of 687691 is 196786.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 687691 - 2³ = 687683 is a prime.

It is a super-2 number, since 2×687691² = 945837822962, which contains 22 as substring.

687691 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 687691.

It is not a weakly prime, because it can be changed into another prime (687641) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343845 + 343846.

It is an arithmetic number, because the mean of its divisors is an integer number (343846).

2⁶⁸⁷⁶⁹¹ is an apocalyptic number.

687691 is a deficient number, since it is larger than the sum of its proper divisors (1).

687691 is an equidigital number, since it uses as much as digits as its factorization.

687691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18144, while the sum is 37.

The square root of 687691 is about 829.2713669240. The cubic root of 687691 is about 88.2668809177.

It can be divided in two parts, 687 and 691, that added together give a triangular number (1378 = T₅₂).

The spelling of 687691 in words is "six hundred eighty-seven thousand, six hundred ninety-one".